The present invention relates to a method for determining an exciter conductor spacing of an exciter conductor from a sensor element of a calibratable magnetic field sensor, as well as to a method for calibrating a sensor element of the magnetic field sensor and usage of an exciter conductor structure for determining the exciter conductor spacing, as well as a respective calibratable magnetic field sensor. In particular, the magnetic field sensor can be a horizontal or lateral Hall sensor having one or several sensor elements.
For determining the sensitivity of a magnetic field sensor, a magnetic field having a known magnetic flow density can be generated at the location of the sensor via a coil or an exciter conductor. The sensitivity of the sensor can then be inferred via the change of the output signal of the magnetic field sensor. If the magnetic field sensor is a Hall sensor, the output signal can be a respective hall voltage. Thus, in a magnetic field sensor based on a Hall sensor, the sensitivity of the Hall sensor can be inferred by a change of the Hall voltage that can be caused by a change of the magnetic flow density in the sensor element. In integrated magnetic field sensors that are integrated in a semiconductor substrate, such a coil or exciter conductor structure can also be implemented in an integrated manner on the semiconductor chip. The mode of operation of such exciter conductors for Hall sensors is described, for example, in patent specification DE 10 2007 041 230.
In integrated coils or exciter conductor structures, but also in discrete exciter conductor assemblies, the problem can arise that during production of the magnetic field sensor in a semiconductor substrate the individual layer structures are subject to the typical process variations as they occur during the production of semiconductor devices. In a semiconductor device, these process variations can generally be higher in a vertical direction than in a lateral direction with respect to a semiconductor substrate surface. Accordingly, a spacing value of an exciter conductor structure which is implemented, for example as conductive trace above or beside a magnetic field sensor in a semiconductor chip or semiconductor substrate, can deviate from an ideal spacing value aimed at during production. Since the position or effective spacing of the exciter line to the actual sensor element of the magnetic field sensor enters a calibration of the magnetic field sensor by generating a defined magnetic field by means of an electric exciter conductor structure, an inaccurate calibration of the magnetic field sensor can result. Normally, a known current is impressed into the exciter conductor structure during calibration, such that a predetermined magnetic calibration flow density that can be traced back to the exciter line is generated at the location of the sensor element of the magnetic field sensor to be calibrated. Here, the calibration magnetic field is adjustable in a defined manner, for example via the impressed current, the geometry or characteristics of the exciter line, i.e. its height, width, thickness, material as well as its relative position, i.e. its spacing to the sensor element. If the sensor element is, for example, a Hall sensor, the sensor element can be calibrated by determining and allocating the associated Hall voltage. The known magnetic calibration flow densities generated at the location of the sensor element can be allocated to the respective Hall voltages measured with the sensor element of the magnetic field sensor, whereby the sensor element and hence the magnetic field sensor can be calibrated.
FIGS. 6a-b schematically show the top view and sectional view of a conventional lateral Hall sensor in a semiconductor substrate 4. The lateral Hall sensor element 1 has four contact terminals 1a-1d that are provided for electric connection to an external control circuit. A Hall sensor element that is arranged in parallel to a chip surface 4a—the x-y plane—and that can measure a magnetic field component perpendicular to the chip surface is referred to as horizontal or lateral. The lateral Hall sensor 1 can be excited with an exciter line 2 arranged around the sensor and implemented in a coil-like manner, as illustrated in FIG. 6a. This means that a predetermined calibration magnetic field can be generated in the sensor element by impressing a defined current with the help of the exciter conductor. In a lateral or horizontal Hall sensor, the above-mentioned process tolerances when producing the semiconductor device have hardly any influence on the flow density generated by the coil at the location of the lateral Hall sensor, since the spacing A between a sensor center point (sensing center point) S and the exciter line or the coil 2 shown in the sectional view of FIG. 6b is many times greater than the process tolerances during production in lateral direction.
FIGS. 7a-b illustrate the schematic top view and section through a vertical Hall sensor. Vertical means a plane perpendicular to the plane of the chip surface 4a, i.e. vertical to the x-y plane. The vertical Hall sensor element 7 illustrated schematically in FIGS. 7a-b comprises, for example, five contact areas 7a-7e along the main surface 4a of the active semiconductor area. Vertical Hall sensors that can measure a magnetic field component in parallel to the chip surface (x-y level) can also be excited specifically with a current flow by an exciter conductor 2 for calibration. The exciter conductor can, for example, be routed directly over the sensor or in the vicinity past the sensor, as shown schematically in FIG. 7a. In a vertical Hall sensor, the above-mentioned process tolerances can have a particularly strong effect during the production of the Hall sensor, since a spacing A between the center point S of the sensor and the exciter conductor 2 can be in the same order of magnitude as the process tolerances. As a consequence, the sensitivity of vertical Hall sensors can frequently only be determined with relatively low accuracy. Calibration can be inaccurate and comprise variations when same is not performed with an actual spacing value A, but merely with an assumed exciter conductor spacing, which is in reality frequently not completely correct or inaccurate due to the process tolerances during production.
Thus, process tolerances during production can have a particularly strong effect with respect to the substrate surface in vertical direction, such that the actual spacing or the effective relative position can deviate from the actually assumed spacing value of an exciter conductor by which the calibration of the sensor element is performed. Due to that, the sensitivity of such sensors, in particular of vertical Hall sensors, can frequently only be determined with low accuracy.
Thus, it would be desirable to be able to accurately and reliably determine the exciter conductor spacing between an exciter line and a sensor element of a magnetic field sensor in order to obtain improved calibration and hence increased sensitivity of the magnetic field sensor.